Liquid level indicator



LIQUID LEVEL INDICATOR Filed March 9, 1951 l 6 Sheets-Sheet l July 131954 J. P. M. DROIN ET AL 2,683,371

LIQUID LEVEL INDICATOR Filed March 9, 1951 6 Sheets-Sheet 2 Figz L July13, 1954 Y 4.1. P. M. DRolN ETAL 2,683,371

. LIQUID LEVEL INDICATOR Filed March 91951 y 4 s sheets-sheet sv QT IgJuly 13, 1954 V -J. P. M. DRolN ET AL 2,683,371 LIQUID LEVEL INDICATOR lFiled March 9, 1951 l e sheets-sheet 4 u 5 l z IU Toward? 4 ENT@ causa,ea/15 /CPa/vcoyfs a/vnorivmf Har-N135 `LIQUID LEVEL INDICATOR FiledMarchv '9,' 1951 e sne'eIs-sheet 5 /IVVEN 70H July 13,'1954 L J. P. M.lDRolN x-:T A1.

LIQUID LEVEL INDICATOR 6 Sheets-Sheet 6 Filed March 9, 1951 Figlia.

Patented July 13, 1954 LIQUID LEVEL INDICATOR Jacques Paul Marcel Droin,Lyon,

and Franois Robert Bonhomme, Gennevilliers, France, assignors to Societede Brevets pour les Applications de lElectronique (S. B.

A. E.) Asnieres,

(Seine), France, a society of France Application March 9, 1951, SerialNo. 214,77 6

Claims priority, application France March 16, 1950 11 Claims.

The present invention relates to apparatus for indicating at a distancethe level oi a liquid in a tank or other vessel.

The object of our invention is to provide an apparatus of this kindwhich is better adapted to meet the requirements of practice than thoseexisting at the present time.

Preferred embodiments of our invention will be hereinafter` describedwith reference to the accompanying drawings, given merely by way ofexample and in which:

Fig. 1 is a diagrammatic perspective view illustrating the principle ofour invention.

Fig. 2 diagrammatically shows one of the electric circuits of theapparatus of Fig. 1.

Fig. 8 is a perspective View on an enlarged scale of one of the liquidlevel sensitive elements of this apparatus.

Fig. 4 shows the electric lay-out of our apparatus.

Figs. 5, 6 and 7 are a bottom plan view, a vertical sectional View and aperspective view of another kind of liquid level sensitive element foruse according to our invention.

Fig. 8 is a diagrammatic vertical sectional View of a modification. l

Figs. 9 and l0 are similar views relatmg to other modications.

Fig. 11 is a perspective view of still another modification. l

Fig. l2 is a horizontal cross-sect1on of st1ll another modification.

Fig. 13 is a perspective View of still another modiiication.

Figs. 14 and l5 are a perspective view and a vertical section of anotherembodiment of our in- 'vention.

. On this screw is engaged a support S guided by two vertical rods 4.Support s carries two liquid level sensitive variable electricalreactive elements I and 2, carried at slightly different levels withrespect to each other. For instance, element 2 is located at a levelslightly above that f of element I.

The expression liquid level sensitive variablek electrical reactiveelement means an element which reacts diiierently, from an electricalpoint of view, according as itis above or below the liquid level. By wayof example, in the embodiment n illustrated by' Fig. 1,Y these elementsare constituted by capacitors. Each of these capacitors is essentiallyconstituted, in this construction, by two metal grids parallel to eachother and which form the conductors of this capacitor, Whereas thedielectric is constituted by the space between these grids. Oi course,the capacitance of such a capacitor is very different according as it isimmersed in the liquid or located in the atmosphere above the level ofthis liquid.

Screw 3 is rotatable in journals located at the top and bottom oi tank Tand it is driven by an electric motor 5. Thus, rotation of this motor inone direction or the other causes support S to move upwardly ordownwardly in tank F.

The movement of motor 5 is transmitted through a shaft F to a reducinggear 6 and thence through a shaft F1 to screw 3.

The movement of shaft F1 is transmitted through a speed reducingmechanism I0 to dials D1 which indicate the height of the liquid levelin tank T.

The indications of dials D1 are teletransmitted through suitablecircuits including devices I I, I2, I3, I4, for instance of the Selsyntype, to dials I5, I6, Il, I8.

Now, operation of electric motor 5 is controlled as follows:

Running of this motor in either direction is controlled by two circuitsC and Ca (Fig. 4) so that when no current is iiowing through either ofthese circuits, the motor is stopped whereas, when current is owingthrough circuit C, motor 5 is made to run in the direction which causesthe support S of elements I and 2 to move downwardly and when current isiiowing through circuit Ca, motor 5 is made to run in the oppositedirection, which causes support S` to move upwardly.

The essential elements of circuit Ca are shown by Fig. 2. This circuitincludes the lower liquid level sensitive element, to wit capacitor I.It further includes a similar capacitor B of the same capacitancelocated in xed position at the bottom of tank T so as to be constantlyimmersed in the liquid of this tank. Both of these capacitors I and 8have one plate connected with a source of low frequency alternatingcurrent 2|. Each of the two other plates of said capacitors is connectedwith the grid of a triode 22, 23 respectively. If both of the capacitorsI and 8 are in the same medium, i. e. if capacitor 8 is below the liquidlevel (as it is normally), the voltages on these grids are in phase andpractically equal (the differences being due to unequalities in thecharacteristics of the conductors through which they are connected withtheir respective capacitors). The cathode voltages of tubes 22 and 23,balanced by means or a variable resistance 24, are transmitted to thegrid and the cathode respectively oi a tube 25 which therefore gives apractically zero voltage across its plate circuit under normalconditions. But if capacitor i, due to a drop of the liquid level intank T, ceases to be immersed in the liquid, its capacitance ceases tobe equal to that of capacitor il. The grid voltage of tube 22 increasesand a low frequency voltage is produced across the plate circuit ofplate 25. This voltage is ampliiied (Fig. e) and serves to energizemotor 5 in one direction.

It is pointed out that this arrangement o crates the electric motor inresponse to an unbalance between the actual capacitances of capacitors Iand 8 as is produced when capacitor ceases to be immersed in the liquid,irrespective or" the absolute value of the variation of capacitance ofelement I when it passes from the liquid into the atmosphere about thelevel or said liquid. Thus, our apparatus can be applied to differentliquids.

The other circuit CCL includes movable capacitor 2 (mounted on support Sslightly above the level of capacitor I) and a fixed capacitor 9 locatedat the top of tank T and of a capacitance equal to that of capacitor 2(when said element E is above the liquid level). It is similar inarrangement with circuit C but connected with motor 5 in such mannerthat any unbalance between the actual capacitances of elements 2 and e(due to the fact that the liquid level rises in tank T and passes aboveelement 2) produces a current which operates motor 5 in the directionwhich moves the support of capacitors I and 2 upwardly.

It will be readily understood that, with such a system, support S isautomatically displaced by motor 5 so that capacitors I and 2 are alwaysrestored to a position such that one of them is just below the liquidlevel and the other just above this level. As the rotation displacementsof the shaft F of motor 5 are also transmitted to the indicating meansconstituted by dials D1 and i5, SG, Il, I8, these means constantlyindicate the height of the liquid level in tank 'I'.

Fig. e is a more complete disclosure of the electric lay-out of thedevice. Circuits C and Ca include the saine elements, designated by thesame reference numerals (with ind-ez; d for the elements of circuit Ca).Taking for instance circuit C it comprises, in addition to the elements22, 23 and 25, already referred to with reference to Fig. 2, amplifyingand detecting means {5t-3l which supply a positive direct voltage at 38when there is an unbalance between capacitors i and 8. rI'his voltagecauses current to flow through a tube 4e which, under normal conditions,is negatively biased beyond cut-on". The current thus produced actuatesa relay E for operating motor 5 in one direction. An electric lamp 66 isswitched on when motor 5 is thus running.

An electric lamp 48 is switched on when motor 5 is stopped and support Sis stationary in a position indicating the liquid level.

The source of low frequency alternating current 2I is common to bothcircuits C and Cc.

All this electric system is enclosed in a box shown at 1 on Fig. 1.

Fig, 3 shows an embodiment of one of the capacitors above referred to.The conductor elements are constituted by grids 25 and each consistingof parallel thin metal wires and carried by insulating supports 29mounted on a base plate 28 provided with holes for an easy now of theliquid therethrough.

Figs. 5 to 7 show another, and preferred, embodiment of a capacitor tobe used in a device according to our invention.

This capacitor includes a nrst electrode having a horizontal conductorplate 4I and a multiplicity or metallic points d3 the lower ends ofwhich are all located in the same horizontal plane. The other electrodeis constituted by another horiuontal conductor plate 4": secured throughinsulating rods to plate 4I at a distance under the horizontal plane ofthe lower ends of points 5.3.

A grounded screen 45, provided with holes for the passage of point-s 3,is interposed between plates 4I and ITI, this screen being separated byan insulating plate 41 from plate 4I.

Plate 4i is provided with a multiplicity of holes for the flow of theliquid therethrough, in order to facilitate displacements o said platein the liquid.

The advantage of this construction is that the forces due to the surfacetension of the liquid, which, in constructions of the kind or" that ofFig. 3, tend to oppose vertical displacements of the capacitor when itselements are to pass through the liquid free surface are eliminated.

Fig. 8 shows a modification of the construction of Fig. 1 according towhich capacitors I and 2, instead of being located directly in contactwith the liquid and gas (air) present in tank T, are located in aiiuidtight vertical chamber limited by a wall 5E! and containing supportS and screw 3. Wall 50 is made of an insulating material. The electricallines of force between the plates of the capacitors extend partly to theoutside o the chamber limited by wall 50 and the presence of liquid atthe level of the space between these plates of course modifies thecapacitance of th capacitor which is concerned.

In the modification of Fig. 9, which is based upon the same principle,the variation effect is improved by providing, slidable verticallyaround wall 5D, a float 5! of a material having a dielectric constant ashigh as possible.

The construction of Fig. 10 is similar to that of Fig. S, but furtherincludes an insulated metal electrode 52 surrounding wall 50 intended toimprove the sensitiveness of the system.

In the modification of Fig. 11, the capacitors are still located insidea closed chamber limited by a wall 56a of an insulating material. Butthe inner and outer faces of this wall are in the form of square threadscrews and the plates 53, 54 and 55, 5S of the two capacitors (analogousto capacitors I and 2 of Fig. l) are applied against the top and bottomfaces oi the screw thread, both or" the capacitors receiving bodily arotation movement from rod 3, along which they can slide axially so asto move helically along wall 5M. Thus liquid is present between theplates of the capacitors. The lines of force between the plates oi thecapacitors are vertical.

In the modification of Fig. 12, the plates 5?-53, 59-58 of thecapacitors, instead of being horizontal, are vertical and slide alongthe sides or" vertical grooves 6I provided on opposite sides ofinsulating wall 5t. In this case also, liquid is present between theplates of the capacitors. The lines of force are horizontal.

In the embodiment of Fig. 13, the two capacitors Ia and 2c are locatedon the outside of the tank T which communicates at 'HI with a fiatvertical tube t so that the liquid in tube t is at the same level as inthe tank. The two condensers, which are driven simultaneously by twoscrews 3a and 3b have their respective plates (such as 51a and 58a forone condenser, only one plate, 60a, of the other condenser being visibleon the drawing) located on either side of tube t, so that in this casealso the liquid is present between the plates of each capacitor.

In the description of Figs. to 13, we have only shown the movingcapacitors, to wit I and 2 in Fig. 10, 53-54 and 55-56 in Fig. 11, 51-58and 59-60 in Fig. 12, Ela-58a and 60a in Fig. 13, because the structure,location and manner of moving these capacitors constitute thedistinctive features of these modifications. But of course the indicatordevice, in any of these modifications, includes two fixed capacitorssimilar in structure to the two above mentioned moving capacitors,respectively, and located similarly to the reference capacitors 8 and 9of Fig. l. As for the electric circuits, motor and indicator means, theyare similar to those described with reference to Figs. 1 to 4.

In all the above described embodiments of our invention, the liquidlevel sensitive variable electrical reactive elements l and 2 consist ofcapacitors. It should be well understood that our invention is notlimited to this case. For instance, Figs. 14-15 and 16 show examples ofvariable inductance elements.

In the embodiment of Fig. 14, the left hand side liquid level sensitiveelement includes apparatus characterized by an annular ring 63 ofmagnetic material carrying two windings `64 and 65 to form a magneticcircuit. Between these windings, there is a space in ring 63 forming agap in the magnetic circuit and in this space there is verticallyslidable a magnetic member 66, preferably held by a spring 67. When thisdevice is located outside of the liquid, member '66 is in its lowerposition and the gap in the magnetic circuit 63 exists. On the contrary,when the device comes into contact with the liquid, the upward thrustexerted on member 66 causes it to close the gap in said magnetic circuit63.

Therefore, if an alternating current is fed to winding 64, thealternating current collected from winding 65 is different according asthe device is above or below the liquid level.

The other element carried by support S (on f the right hand sidethereof) is similar, but its magnetic circuit is located at a levelslightly above that of core 63.

Both of the primary windings of these elements are fed with alternatingcurrent, for in I stance of low frequency, say 1,000 periods. Thecurrents iiowing through the secondary windings are supplied to a doubleprimary of a transformer so as to give zero current in the secondarythereof when each element is in the same state as the correspondingreference element (one at the top, the other at the bottom of the tank),i. e. when one of the liquid level sensitive elements is just above theliquid level and the other just below this level. When the liquid levelvaries, there is an unbalance in one of the circuits and the transformerdelivers a current in one direction or the other to operate the motorwhich drives screw 3 and the indicating means.

In the modication of Fig. 16, the windings ll and 65 are carried by aportion 69 of the magnetic circuit located inside a fluidtight chamberseparated from the inside of the tank by a partition 56h. This portion69 of the magnetic circuit is constituted by a magnet and therefore 6holds, through partition 50h, the remainder t8 of the magnetic circuit.

In a general manner, while we have, in thc above description, disclosedwhat we deem to be practical and eiiicient embodiments of our invention,it should be well understood that we do not wish to be limited theretoas there might be changes made in the arrangement, disposition and formof the parts without departing from the principle of the presentinvention as comprehended within the scope of the accompanying claims.

What we claim is:

l. A device for measuring and indicating the height in a vessel of thelevel of the surface of separation of a liquid and another fluid locatedabove said liquid, which device comprises, in combination, a supportwithin the vessel and movable vertically with respect to said vessel,two liquid level sensitive variable electrical reactive means carried bysaid movable support within the vessel and in xed position with respectto said movable su-pport, one of said means being located at a levelslightly above that of the other, two reference electrical reactivemeans similar to said two nrst mentioned means respectively, mounted,one in a position constantly above the liquid level and the other in aposition constantly below the liquid level, an electric motor, meansoperative by said motor for moving said support upwardly and downwardly,indicator means operative by said motor in response to the workingthereof, and two electrical circuits for controlling said motor, one ofthese circuits including the first mentioned reference means and thevariable means located at a level above that of the other variable meansand the other circuit including the second mentioned reference means andthe variable means located at a level below that of the other variablemeans, each of these circuits being adapted to supply no current whenthe reference and variable means thereof are located both between thetop and bottom levels of the same medium and to supply current when thevariable means thereof is above or below the level between the mediumsin a direction away from the reference means thereof, the iirstmentioned circuit being arranged to operate said motor in the directionwhich moves said support upwardly and the second mentioned circuit beingarranged to operate said motor in the direction which moves said supportdownwardly.

2. A device for measuring and indicating the height in a vessel of thelevel of the surface of separation of a liquid and another fluid locatedabove said liquid, which device comprises, in combination, a supportwithin the vessel and movable vertically with respect to said vessel.two liquid level sensitive capacitors within the vessel and carried bysaid movable support in fixed position with respect to said movablesupport, one of said capacitors being located at a level slightly abovethat of the other, two other liquid level sensitive capacitors similarto said two rst mentioned capacitors respectively, mounted in fixedposition with respect to said vessel, one in a position constantly abovethe liquid level and the other in a position constantly below the liquidlevel, an electric motor, means operative by said motor for moving saidsupport upwardly and downwardly, indicator means operative by said motorin response to the working thereof, and two electrical circuits forcontrolling said motor, one of these circuits including the firstmentioned iixed capacitor and the movable capacitor located at a levelabove that of the other movable capacitor and the other circuitincluding the second mentioned fixed capacitor and the movable capacitorlocated at a level below that of the other moY Jole capacitor, each ofthese circuits being adapted to supply no current when the iired andmovable capacitors thereof are located both in the same medium and tosupply current when the movable capacitor thereof is in a mediumdiiierent from the fixed capacitor thereof, the first mentioned circuitbeing arranged to operate said motor in the direc-- tion which movessaid support upwardly and the second mentioned circuit being arranged tooperate said motor in the direction which moves said support downwardly.

3. A device according to claim capacitors are located in said vessel.,in direct contact with the liquid and other fluid preset therein.

4. A device according to claim 2 in which said capacitors aro located insaid vessel, direct contact with the liquid and other present therein,each oi said capacitors being constituted by two superposed gridsforming the electrodes thereof.

5. A device according to claim in which said capacitors are located insaid vessel, in direct contact with the liquid and other iluid presenttherein, each of said capacitors being co sttuted by an upper conductorplate and a plurality of pointed conductor rods ig downwardly from saidpoint, a layer ci an inst ting material applied against the under facesaid plate, a screen carried on the under side said layer provided witha plurality or" holes c; a s passage of said pointed rods withclearance, and a plate parallel to the first inentioned plate locatedbelow the level of the lower ends of said rods.

6. A device for measuring and indicating the height in a vessel oi thelevel of the surface oi separation or" a liquid and another rluillocated. above said liquid, which device conc. ises, in combination, aninsulating partition forming a vertical rluidtight chamber in saidvessel, said partition being surrounded by and in contact with saidliquid and said fluid, a support positioned in and movable vertically insaid chamber, two liquid level sensitive capacitors carried by saidmovable support in position with respect thereto and n close proximityto the inner surface of said partition so that lines of force willextend partly to the outside of the chamber, one oi said e other, twoother s similar to said two first mei y ctiv mounted in fixed positionin said chan i, one in a position constantly above the liquid level andthe other in a position constantly below the liquid level, said othercapacitors being mounted in said chamber so that lines oi force willextend to the outside or" said partition, an electric motor, meansoperative by motor for moving said support upwardly doa -wardiy,indicator means operative by motor in to the pense working thereof, andtwo electA controllingr said motor, one of these cluding the iirstmentioned cv acitor and the movable capacitor located at a level abovethat of the other movable ce cito-f and the other circuit including thesecond mentioned fixed capacitor and the movable capacitor located at alevel below that o the other movable capacitor, each of these circuitsbeing adapted to supply no current when the fixed and movable capacitorsthereof are located both between the top and botto-in levels oi the samemedium and to supply current when the movable capacitor thereof is aboveor below the level between the mediums in a direction away from theiixed capacitor thereor", the first mentioned circuit being arranged tooperate said motor in the direction which moves said support upwardlyand the second mentioned circuit bei, arranged to operate said motor in.i which moves said support downv' wardly.

7. A device according to claim 6 further including a sleeve of aconductor material carried by said vessel around said partition.

8. n device according to claim 1 in which each of said means includesapparatus forming a magnetic circuit having a gap therein and a primaryand secondary winding on opposite sides of the gap, and a magneticmember movable with respect to said magnetic circuit normally locatedoutside oi said gap and responsive to the buoyant thrust oi liquid so asto fill said gap when the means in question is immersed in said liquid.

9. A device according to claim 2 in which the wall ci said vessel formsat least one i'iat hollow ridge the inside of which forms a portion ofthe inside oi id vessel intended to receive liquid, said capacitorsincluding each two plates located on opposite faces oi said ridgerespectively and slidable thercaiong, so that the lines of force extendbetween these two plates pass across the id present inside said ridge.

'i device for measuring and indicating the a quid in a tank, whichdevice comprises, in coin. iation, a -dat tube extending verticallyalong said tanl; on the outside thereof, this at tube communicating withthe inside of said tank so that the liquid surface is at the same levelin said tube as in said tank, a support movable vertically along saidiiat tube, two liquid level sensitive capacitors carried by said movablesupport in xed position with respect thereto, one of said capacitorsbeing located at a level slightly above that of the other, two otherliquid level sensitive capacitors similar to said two first mentionedcapacitors respectively, mounted in xed position with respect to saidtank, one in a position constantly above the uid level and the other ina poron constantly below the liquid level, each ci said capacitors beingconstituted by two plates located on either side of said iiat tube onone edge of said tube, the two 'lrst mentioned capacitors ablesimultaneously along said edges, an elecf" c motor, means operative bysaid motor for ig said supp upwardly and downwardly, indicator meansoperative by said motor in response to the worl g thereof, and twoelectrical circuits for controlling said motor, one of these circuitsincluding the iirst mentioned fixed capacitor and the movable capacitorlocated at a level above that of the other movable capacitor the othercircuit including the second nientioned fixed capacitor and the movablecapacitor located at a level below that of the other movable capacitor,each of these circuits being adapted to supply no current when the ixedand movable capacitors thereof are located both between the top andbottoni levels of the saine medium and to supply current wien themovable capacitor thereof is above or below the level between themediums in a direction away from the fixed capacitor thereof, the rstmentioned circuit References Cited in the file of this patentbeingharranged to operate said motor in the UNITED STATES PATENTSdlrectlon which moves sald support upwardly and the second mentionedcircuit being arranged to Nmber Name Date operate said motor in thedirection which moves 5 2'3 4945 Cohen et al Aug' 1f 1944 said Supportdownwardly. FOREIGN PATENTS 11. A device according to claim 8 in whichsaid magnetic circuits are located Iin the vessel in Nuglag GerglrlgtrySepjagelgm direct contact with the 11qu1d present therein. m 441,576Great Britain Jan 22, 1936 114,930 Sweden Sept. 18, 1945

